1. Field of the Invention
This invention relates to a special purpose calculator. More particularly, it relates to such a calculator which is especially adapted for use by tradespeople and others who are required to do a substantial amount of calculation involving numbers expressed as fractions. Most especially, it relates to such a calculator which will also handle calculations involving numbers expressed in feet and inches.
2. Description of the Prior Art
Hand-held calculators have assumed a ubiquitous role in a wide variety of occupations. Special purpose calculators have been made available for scientific, financial and statistical calculations. It is also known to provide a calculator which will convert measurements expressed in one unit of measurement to a different unit of measurement, such as from inches to centimetres or inches to feet automatically. One such conversion calculator is describe in the publication entitled "MOS/LSI Data Book" (Santa Clara, California, National Semiconductor Corporation, 1977), pages 8-56-8-65.
In a substantial number of occupations, it is necessary to carry out calculations involving fractional numbers. Such calculations are common in the construction trades, in machining, and the garment trades. Despite the worldwide acceptance of metric measurements, most measurements of length in these and other trades in the United States continue to be made in inches and feet, with measurements less than one inch in length being expressed as fractions. When calculations involving such measurements are to be carried out using prior art calculators, it has been necessary to convert the fractions to decimals. Doing so adds another level of calculation, which is confusing to the user. As a result, a fairly high percentage of calculations involving measurements of length in inches and feet continue to be performed manually. If such calculations could be conveniently carried out with an electronic calculator, errors in these calculations would be reduced.